Stencil duplicators

ABSTRACT

The specification discloses a stencil duplicator including a freely rotatable bar mounted parallel to and adjacent the rising side of the top cylinder so that the lower face of a stencil may roll thereover during application to the duplicator cylinder. In the preferred embodiment the bar is adjacent a further surface which may be in the form of a rib in the top cover of the duplicator so that a tortuous stencil path is defined by the bar and further surface.

In venlor Leonard wunr My B wm. Cmb hMm Allorrwyl STENCIL DUPLICATORS This invention relates to an improvement for use in stencil duplicators, particularly twin-cylinder stencil duplicators, which enable easy and rapid mounting of a stencil on the stenoil carrier of the duplicator.

Conventionally a stencil is fitted to the stencil carrier of a twin-cylinder duplicator by having its heading strip clamped at its top edge to the stencil fixing clamp of the duplicator and then being wiped onto the stencil carrier of the duplicator while the cylinders are rotated slowly by hand. During rotation of the cylinders the stencil carrierpasses between the top cylinder and the hand of the operator and is thus wiped or pressed into contact with the stencil carrier. This has the disadvantage that, whereas the stencil is pressed into firm engagement with the stencil carrier near the stencil centerline, the edges of the stencil are not pressed into contact and frequently are subject to puckering and creasing. Using this method of attachment of the stencil the extent to which the stencil is laid on the stencil carrier without creasing will depend upon the skill of the duplicator operator. 4

It is an object of the present invention to provide an improvement in stencil duplicators in the form of an apparatus which facilitates laying a stencil on the stencil carrier without creasing or puckering.

According to the present invention, we provide a stencil duplicator having a cylinder on which, in use of the duplicator, a stencil is to be laid, wherein a cylindrical surface having its axis parallel to the axis of said cylinder, is positioned on that side of the vertical plane passing through the axis of symmetry of the cylinder at which the surface of the cylinder ascends during normal operation of the duplicator, such cylindrical surface being arranged to be freely rotatable by contact with a stencil passing therearound when the stencil is being laid onto the cylinder so that a stencil being fed onto the cylinder will be partially supported by the cylindrical surface.

Preferably a further surface is adapted to be positioned in association with said rotatable cylindrical surface so that said further surface lies outside the tangent plane common between the upper part of the surface of said duplicator cylinder and the upper part of said cylindrical surface.

Conveniently said further surface is defined on a downwardly extending rib having its axis parallel to the axes of said rotatable cylindrical surface'and said duplicator cylinder, said downwardly extending rib being formed in a pivotable member of said duplicator. Suitably said pivotable member comprises a top cover of the duplicator. Desirably said rotatable surface comprises a cylindrical rod freely rotatably mounted in the frame of said duplicator.

By providing ready laying on of a stencil without the need for manual smoothing on by the duplicator operator, the apparatus of this invention enables a stencil to be laid on the stencil carrier while the duplicator is being rotatedunder its own power rather than being rotated by hand.

In order that the present invention may more readily be understood the following description is given merely by way of example, of one embodiment of stencil laying apparatus of this invention. Reference will be made to the accompanying drawings in which:

FIG. 1 is a somewhat schematic side view of a stencil duplicator incorporating the stencillaying apparatus of the in- 'vention, the duplicator top cover being shown in section; and

FIG. 2 is a view, similar to FIG. 1, but showing the duplicator top cover in its closed position and a stencil and backing sheet being fed on the stencil carrier.

Referring now to the drawings, FIG. 1 shows a stencil and backing sheet 1 clamped on studs 2 of a stencil fixing bar 3 and held in position on the studs by the spring biased flap 4 of the stencil fixing clamp. A stencil laying bar 5 comprises a rotatably mounted cylindrical bar journaled in bearing mountings formed in the frame of the duplicator. The stencil and backing sheet 3 are allowed to rest on the laying bar 5,

The duplicator is provided with a top cover 6 comprising an end or handle portion 7 and a straight rib 8 formed in the under surface thereof and having a lower convex face 8a. The main body of the top cover 6 is secured by means of screws to a hinge portion 9 pivoted at 10 to the main frame of the duplicator. When the top cover 6 of the duplicator is moved to its closed position, as illustrated in FIG. 2, the surface 8a of the rib 8 engages the backing sheet of the stencil between the stencil laying bar 5 and the nearest point of contact of the stencil 1 with the top cylinder 11 of the duplicator. In order to effectsuch action of the rib 8 and laying bar 5 on the stencil, the rib 8 is so positioned and shaped that when the top cover 6 is closed the surface 8a of the rib lies below the tangent plane common to the upper part of the surface of the cylinder 11 and the upper part of the surface of the stencil laying bar 5. The particular positioning of the rib 8 and the stencil laying bar 5 serves two purposes, namely to prevent the backing sheet from flying up out of contact with the stencil while passing over the laying bar 5, and also to provide a tortuous path for the stencil and backing sheet which has the result that the rigidity of the backing sheet, in tending to resist passage round the sharp bends created by the presence of the rib 8 and bar 5, induces tension in the run of the stencil and backing sheet between the fixing bar 3 and the rib 8. This is most important during the initial laying of the stencil since once the leading part of the stencil has been properly and smoothly applied the final few inches of the leading end of the stencil fall properly in place against the sticky ink covered stencil carrier after the trailing end has passed the laying bar 5. The combined effect of the holding down of the backing sheet and also of the induction of tension in the stencil being laid is that the stencil is urged on to the surface of the stencil carrier under tension and is smoothed down" by the effect of the tension in the backing sheet. As explained above the conventional method of laying the stencil on the stencil carrier requires manual smoothing of the stencil on to the carrier by the operator.

With the tensioning action of the bar 5 and rib 8 of this invention the lateral edges of the stencil and backing sheet, as

well as the center thereof, are held under tension during laying on of the stencil. Further, the tension is uniform across the stencil and thus puckering and creasing are eliminated. Clearly then, using the combination of the rib 8 and bar 5 provides a means of laying the stencil on the stencil carrier both ithout puckering or creasing and independently of the skill and it will be appreciated that the stencil is in contact with the and expertize of the operator of the duplicator.

The particular arrangement of the rib 8 on the underside of top cover 6 enables rapid and simple insertion of the stencil between the rib 8 and bar 5.

In order more clearly to illustrate the advantages of the apparatus of this invention descriptions will be given below illustrating the laying on of a fresh stencil and backing sheet on the stencil carrier and also an inked stencil which has previously been used and removed from the duplicator and is now to be reinserted for further use.

When laying a fresh stencil on the stencil carrier the duplicator top cover 6 is pivoted to the open position illustrated in FIG. 1, the cut stencil and backing sheet are laid over thelaying bar 5 and the stencil heading is brought up to and placed in clamping relation with the stencil fixing bar 3 in such a manner that the stencil is in contact with the laying bar 5 and the backing sheet is uppermost. The duplicator top cover 6 is then moved to its closed position, illustrated in FIG. 2, after which the proofing lever (not illustrated) i operated and the duplicator rotated under its own power far'one cycle to lay the stencil on the cylinder and, if desired, two or more further cycles for producing a proof copy on the backing sheet. The proofing lever is then moved to its inoperative position and the top cover 6 raised in order to facilitate removal of the backing sheet from the stencil heading, the stencil itself now being in close contact with the stencil carrier. If the duplicator has come to rest with the stencil fixing clamp in an inaccessible position, then the duplicator should be rotated until the fixing clamp is accessible and the backing sheet can be removed from the stencil heading by tearing along on the perforated line. It then only remains to return the top cover 6 to its closed position and the duplicator is ready for use.

In the above description, operation of the proofing lever was necessary since, when laying the stencil on the stencil carrier, it is essential that the conventional printing pressure roller rises to contact the stencil passing round the bottom roller of the duplicator even though no paper is being fed from the sheet feeder between the pressure roller and bottom roller. Since many conventional stencil duplicators incorporate an automatic pressure roller disengaging facility responsive to the lack of a sheet passing through the sheet feeder, it is necessary to override this facility by operation of the proofing lever while the backing sheet is still in contact with the stencil.

The top cover 6 may be left in the closed position or in the open position during the operation of the stencil duplicator, but clearly from the point of view of cleanliness, safety of operation, and noise suppression, it is advisable to run the duplicator with the top cover closed at all times.

When laying an already inked stencil on the carrier, use of the combination of laying bar 5 and rib surface 80 will almost certainly cause damage to the fabric of the stencil by exerting excessive tension on the stencil, and by exposing the printing face of the stencil to the stationary edge of the rib 8. It should be noted that damage to the stencil by the laying bar 5 is avoided since as previously explained the bar 5 is rotatable about its own axis and therefore exerts a rolling action on the stencil rather than a scraping or sliding action.

The procedure for laying an inked stencil is therefore as follows. The top cover 6 is moved to its open position, the inked stencil is placed over the laying bar 5 and the heading clamped onto the stencil fixing bar 3 such that the printing on the stencil reads correctly when viewed from below. Care should be taken to ensure that excessive slack is not evident in the run of the stencil between the laying bar 5 and stencil heading, and then the duplicator is rotated through one cycle in order to lay the stencil on the carrier. The weight of the part of the limp stencil hanging from the laying bar 5 serves to maintain the run of the stencil 11 under sufficient tension to permit the stencil to be laid smoothly on the stencil carrier. Thus less tension is required with the limp stencil than with the combined assembly of stencil and backing sheet.

It should be noted that, in this operation the proofing lever is not operated since rising of the pressure roller against the bottom cylinder would ink the printing face of the stencil and would cause undesirable inky patches on the first 20 or so copies run off.

Since no pressure action is exerted by the roller 9 it is only necessary to rotate the duplicator top cylinder 11 until the trailing edge of the stencil 1 has left the trailing bar 5 and falls into contact with the stencil carrier. At this stage, the duplicator is ready for use.

The above description referred to the rotation of the duplicator as being achieved by automatic operation rather than manual, although clearly the operations could have been performed by manual rotation of the duplicator cylinders. In conventional duplicators the rotation, during laying on, was of necessity performed manually and it is therefore felt that the ability to lay the stencil during automatic operation of the duplicator provides a reduction in the time required for laying on of the stencil, and thus constitutes a major advantage of the duplicator employing the apparatus of this invention.

We claim:

1. A stencil duplicator including:

a. a frame;

b. a cylinder carried by said frame for normal rotation in a given direction and having a curved surface on which in use of the duplicator, a stencil is to be laid;

c. a freely rotatable member carried by said frame in spaced relation with respect to said cylinder and defining a cylindrical surface having an axis which is parallel to the axis of said cylinder, said axis of the said cylinder surface bei n laterally spaced from that side of the cylinder at whic the said curved surface is rising during rotation of the cylinder in said given direction;

d. means defining a movable further surface parallel to said axis; and

e. movable means carrying said surface defining means for moving said surface defining means between an out of the way position and an operative position intermediate, and below the tangent plane common to, the upper part of the said curved surface and the upper part of said cylindrical surface, whereby a stencil and backing sheet being fed onto the said curved surface of said cylinder may pass between said cylindrical surface and said further surface means with the said stencil in contact with said cylindrical surface to cause rotation of said cylindrical surface by frictional contact therewith during feeding onto said curved surface and with said backing sheet in contact with said further surface means.

2. The duplicator of claim 1, wherein said further surface means comprises a pivotable member of the duplicator, having a rib extending downwardly therefrom and incorporating said further surface, said rib extending parallel to the axis of said cylindrical surface.

3. The duplicator of claim 2, and wherein a top cover of the duplicator forms said pivotable member. 

1. A stencil duplicator including: a. a frame; b. a cylinder carried by said frame for normal rotation in a given direction and having a curved surface on which in use of the duplicator, a stencil is to be laid; c. a freely rotatable member carried by said frame in spaced relation with respect to said cylinder and defining a cylindrical surface having an axis which is parallel to the axis of said cylinder, said axis of the said cylinder surface being laterally spaced from that side of the cylinder at which the said curved surface is rising during rotation of the cylinder in said given direction; d. means defining a movable further surface parallel to said axis; and e. movable means carrying said surface defining means for moving said surface defining means between an out of the way position and an operative position intermediate, and below the tangent plane common to, the upper part of the said curved surface and the upper part of said cylindrical surface, whereby a stencil and backing sheet being fed onto the said curved surface of said cylinder may pass between said cylindrical surface and said further surface means with the said stencil in contact with said cylindrical surface to cause rotation of said cylindrical surface by frictional contact therewith during feeding onto said curved surface and with said backing sheet in contact with said further surface means.
 2. The duplicator of claim 1, wherein said further surface means comprises a pivotable member of the duplicator, having a rib extending downwardly therefrom and incorporating said further surface, said rib extending parallel to the axis of said cylindrical surface.
 3. The duplicator of claim 2, and wherein a top cover of the duplicator forms said pivotable member. 